Cable-Driven Four-Bar Link Leg Mechanism

ABSTRACT

A leg mechanism includes an articulated leg system, a passive device and a cable. The articulated leg system has a leg portion. The passive device is coupled to the articulated leg system and is configured to apply a first force to a portion thereof. The cable is coupled to the articulated leg system and is configured to apply a second force, in opposition to the first force, to a portion thereof. When the cable is drawn away from the articulated leg system, the second force moves the leg portion in a first direction. When tension is released from the cable, the passive device exerts the first force so as to move the leg portion a second direction that is opposite the first direction.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of Ser. No. 16/645,370, filed onMar. 6, 2020, which is a U.S. National Phase entry of PCT/US18/53385,filed Sep. 28, 2018, which claims the benefit of U.S. Provisional patentapplication Ser. No. 62/565,461, filed Sep. 29, 2017, the entirety ofeach of which is hereby incorporated herein by reference.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with government support under agreement No.FA8650-2-C-7276, awarded by the Department of the Air Force. Thegovernment has certain rights in the invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to leg mechanisms and, more specifically,to a leg mechanism with adjustable extension.

2. Description of the Related Art

Vertical takeoff and landing (VTOL) aircraft, such as helicopters,access landscapes that fixed-wing aircraft are unable to reach. Suchaircraft play a critical role in applications such as the military,emergency air medical services, remote location access and the like.

However, even with VTOL capabilities, VTOL aircraft have landinglimitations due to ground slope and surface obstacles. Because typicalVTOL aircraft have landing gear (including landing skids and landingwheels) in which both sides of the gear extend at an equal distancebelow the aircraft, an uneven landing surface at a location can preventan aircraft from landing at the location.

A similar problem is experienced in robotic applications. While robotsthat are configured to walk can walk along even surfaces, only moreadvanced robots can walk on uneven surfaces. Such robots typicallycontrol each leg separately and require complex calculations for eachstep in order to navigate an uneven surface.

Therefore, there is a need for a leg system that is adapted for use withuneven surfaces.

SUMMARY OF THE INVENTION

The disadvantages of the prior art are overcome by the present inventionwhich, in one aspect, is a leg mechanism that includes an articulatedleg system, a passive device and a cable. The articulated leg system hasa leg portion. The passive device is coupled to the articulated legsystem and is configured to apply a first force to a portion thereof.The cable is coupled to the articulated leg system and is configured toapply a second force, in opposition to the first force, to a portionthereof. When the cable is drawn away from the articulated leg system,the second force moves the leg portion in a first direction. Whentension is released from the cable, the passive device exerts the firstforce so as to move the leg portion a second direction that is oppositethe first direction.

In another aspect, the invention is a two leg system that includes afirst leg mechanism, a second leg mechanism and an actuator. The firstleg mechanism includes a first upright bar that moves vertically inresponse to an amount of tension applied a first cable. The second legmechanism, which is reflectively disposed oppositely from the first legmechanism, includes a first upright bar that moves vertically inresponse to an amount of tension applied a first cable. An actuatorapplies tension to both the first cable and the second cable.

These and other aspects of the invention will become apparent from thefollowing description of the preferred embodiments taken in conjunctionwith the following drawings. As would be obvious to one skilled in theart, many variations and modifications of the invention may be effectedwithout departing from the spirit and scope of the novel concepts of thedisclosure.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS

FIG. 1A is a schematic diagram of a first representative embodiment of aleg system in which the leg is retracted.

FIG. 1B is a schematic diagram of the leg system shown in FIG. 1A inwhich the leg is moderately extended.

FIG. 1C is a schematic diagram of the leg system shown in FIG. 1A inwhich the leg is fully extended.

FIG. 2A is a schematic diagram of a second embodiment of a leg system inwhich the leg is retracted.

FIG. 2B is a schematic diagram of the second embodiment of a leg systemin which the leg is extended.

FIG. 3A is a schematic diagram of a third embodiment of a leg system.

FIG. 3B is a schematic diagram of a fourth embodiment of a leg system.

FIG. 4A is a schematic diagram of a two leg system in which the legs areextended.

FIG. 4B is a schematic diagram of a two leg system in which the legs areretracted.

FIG. 4C is a schematic diagram of a two leg system showing differentialextension and retraction of the legs.

FIG. 5 is a schematic diagram of a spool, sensor and controller.

FIG. 6 is a schematic diagram of a two leg system employed as landinggear for a helicopter.

FIG. 7A is a top plan view of one embodiment of a two leg system.

FIG. 7B is a side elevational view of one embodiment of a two legsystem.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the invention is now described in detail.Referring to the drawings, like numbers indicate like parts throughoutthe views. Unless otherwise specifically indicated in the disclosurethat follows, the drawings are not necessarily drawn to scale. Thepresent disclosure should in no way be limited to the exemplaryimplementations and techniques illustrated in the drawings and describedbelow. As used in the description herein and throughout the claims, thefollowing terms take the meanings explicitly associated herein, unlessthe context clearly dictates otherwise: the meaning of “a,” “an,” and“the” includes plural reference, the meaning of “in” includes “in” and“on.”

Also, as used herein a “cable” can include any type of elongatedsubstantially inelastic (when under tension) yet flexible device and caninclude, for example, a steel cable, a rope, a wire, a cord, a line, astrap, etc., depending upon the specific application. Also, as usedherein, “spring” means any compressive elastic device and can includesuch devices as a coil spring, a torsion spring, a gas (pneumatic)spring, etc.

As shown in FIGS. 1A-1C, one embodiment of an articulated leg system 100includes a first platform coupling joint 110 and a second platformcoupling joint 111. A first lateral bar 120 has a proximal end 121 thatis rotationally coupled to the first platform coupling joint 110 so thatthe first lateral bar 120 is rotatable about the first platform couplingjoint 110 and is constrained to movement along a predetermined plane(i.e., it has one degree of freedom). A second lateral bar 124 isdisposed below the first lateral bar 120 and has a proximal end 123 thatis rotationally coupled to the second platform coupling joint 111 sothat the second lateral bar 124 is rotatable about the second platformcoupling joint 111 and is constrained to movement along thepredetermined plane. An upright bar 128, which acts as a leg portion,has a first bar coupling joint 127 to which the distal end 122 of thefirst lateral bar 120 is hingedly coupled. The distal end 125 of thesecond lateral bar 124 is hingedly coupled to a second bar couplingjoint 129 so that the first lateral bar 120, the second lateral bar 124and the upright bar 128 are all constrained to movement along thepredetermined plane. A passive device 134 (such as a linear spring)couples the first platform coupling joint 110 to the second bar couplingjoint 129. A cable 134 (for example, a steel cable, a plastic cable, arope, a wire, a cord, a line, or a strap, depending upon the specificapplication) is affixed to the first bar coupling joint 129 and engagesthe second platform coupling joint 111. The upright bar 128 movesdownwardly when tension is applied to the cable 134 and moves upwardlywhen tension is released from the cable 134.

As shown in FIG. 1A, in this embodiment, when the tension is releasedfrom the cable 134, the passive device 130 pulls the second bar couplingjoint 129, thereby causing the upright bar 128 to move upwardly. Asshown in FIG. 1B, retracting the cable 134 causes the upright bar 128 tomove downwardly and, as shown in FIG. 1C, fully retracting the cable 134fully extends the leg mechanism 100.

As shown in FIG. 2A, the passive device 130 can couple the first barcoupling joint 127 to the second platform coupling joint 111 and thecable 134 can be affixed to the second bar coupling joint 129. In thisembodiment, applying tension to the cable 134 causes the leg mechanism100 to retract and releasing tension from the cable 134 causes the legmechanism 100 to extend.

In the embodiments disclosed above the passive device 130 pullsinwardly. In other embodiments, a passive device can exert an outwardforce. For example, in one embodiment, as shown in FIG. 3A, the passivedevice 140 can include a gas spring, which exerts an expansive force.

Other types of passive devices may also be used. For example, as shownin FIG. 3B, the passive device can include a torsional spring 150coupled to the first lateral bar 120 and the upright bar 128. Twoindividual articulated leg systems of the type shown could be used inrobotics in which each leg system 100 can be controlled independently.

As shown in FIGS. 4A-4B, a two leg system 200 can employ two articulatedleg systems 100 a and 100 b of the type disclosed above that are affixedto a frame on a platform 210 and both articulated leg systems 100 a and100 b can employ cables 134 a and 134 b that are wound onto a commonspool 220. Winding the cables 134 a and 134 b onto the spool 220 causesboth of the legs to move in a first direction (which is downwardly inthe embodiment shown) by the same amount. Un-winding the cables 134 aand 134 b from the spool 220 causes both of the legs to move in theopposite direction (which is upwardly in the embodiment shown). Thespool 220 can be mounted on a track 222 and moved laterally with respectto a centerline 10. As shown in FIG. 4C, lateral movement of the spool220 causes the articulated leg systems 100 a and 100 b to movedifferentially, which makes this embodiment particularly well suited foruse on an uneven surface. Also, the force is distributed evenly acrossboth of the articulated leg systems 100 a and 100 b and the forceexperienced by the spool 220 is only the difference between the force onimposed on it by the cables 134 a and 134 b.

As shown in FIG. 5 , the spool 220 can be rotated by a motor 230attached thereto. A differential motion actuator 234 (such as a screwdrive of a hydraulic actuator) can drive the spool 220 laterally alongthe track 222. A sensor 242, which could be either a roll indicator or acontact (pressure) sensor, can provide information about the orientationof the platform 210 or the pressure sensed by each leg system 100. Acontroller 240 receives information from the sensor 242 and controls themotor 230 (including the amount and direction of rotation) and theactuator 234 based on the information.

As shown in FIG. 6 , a two leg system 200 can be used as the landinggear for a helicopter 250. With such a system the helicopter 250 canland on a sloped or uneven surface 14, but remain level in relation to ahorizontal 12 reference.

In one embodiment of a cable-driven four-bar linkage mechanism foractuating legs, there are two symmetric followers attached to the bodyof interest and a coupler which extend to form the leg. The mechanism byitself is a one degree of freedom system. Motion in one direction isdriven by a passive spring-like element, for example upward motion canbe achieved through a compression spring pulling along one diagonal. Thereverse motion is achieved through a cable along the opposite directionof the passive element. In the example described above, downward motionof the leg is achieved by retracting the cable (i.e. pulling) and henceextending the spring, and upward motion is achieved by releasing thecable and hence allowing the spring to pull the leg up.

Two such cable-driven mechanisms can be linked with one continuous cableto achieve unique actuation properties. In such a configuration, twopairs of legs are attached to the body of interest and a single cablespans from the diagonal of one leg, through the body, onto the diagonalof the other leg. In such a design one can use an actuator (such as amotor) that reduces/increases the overall length of the cable (forexample a spool) to achieve symmetric downward/upward motion of the twolegs, and a second actuator that changes the center of the cable withoutchanging its length (for example by moving the spool without rotatingit) to achieve an asymmetric movement where one leg moves down and oneleg moves up. This is in distinct contrast to traditional actuationstrategies where a single actuator is used for each one degree offreedom leg.

This embodiment has certain advantages in terms of the loads seen by theactuators. The contact loads coming through the legs are distributed astensile loads on the cable. In this embodiment, where the two legscouple through a continuous cable, the actuator only sees the differencein loads coming from the two legs. For example, if the cable for eachleg is under 100 lbs. of tension, the torsional actuator for the spoolwould require no torque to maintain that position. In contrast, in atraditional design, each actuator controlling the legs independentlywould be required to hold a 100 lb. load. This embodiment also has theadvantage over systems in which the actuator has to be placed in eachleg in that all actuation can be placed within the body to which thelegs are affixed—not in the legs, hence reducing the weight of the legs.

An experimental embodiment is shown in FIGS. 7A and 7B, in which theelements described above are mounted on a frame 300. This embodimentemploys a protective box 221 around the spool. It also includes twodampers 310 (such a rubber dampers), each of which is affixed to adifferent end of the cable 134 a and 134 b, to absorb shock transmittedfrom the vertical legs 128. In this embodiment, the spool end of eachcable 134 a and 134 b is attached to the same side of the spool 220 tothat as the spool 220 is rotated clockwise, then cable 134 a is woundonto the spool 220 and cable 134 b is wound off of the spool 220.Similarly, as the spool 220 is rotated counter-clockwise, then cable 134b is wound onto the spool 220 and cable 134 a is wound off of the spool220. Thus, differential movement of the legs 120 is effected by rotationof the spool 220: if the spool 220 rotates in one direction then theleft leg will go up and the right leg will go down by the same amount,if it is rotated in the opposite direction then the left leg will godown and the right leg will go up by the same amount.

Ground contact forces experienced by the body of interest aretransferred from one leg to the other through the cable connecting them.This has some advantages. For example, the actuators see reduced loadsas the differential motion actuator only needs to hold the difference ofthe loads seen by the two cables.

The differential actuator system offers the advantage that if theactuator fails, the legs will stay in their current position. In devicesin which each leg is actuated independently, a leg will collapse if itsactuator fails.

Although specific advantages have been enumerated above, variousembodiments may include some, none, or all of the enumerated advantages.Other technical advantages may become readily apparent to one ofordinary skill in the art after review of the following figures anddescription. It is understood that, although exemplary embodiments areillustrated in the figures and described below, the principles of thepresent disclosure may be implemented using any number of techniques,whether currently known or not. Modifications, additions, or omissionsmay be made to the systems, apparatuses, and methods described hereinwithout departing from the scope of the invention. The components of thesystems and apparatuses may be integrated or separated. The operationsof the systems and apparatuses disclosed herein may be performed bymore, fewer, or other components and the methods described may includemore, fewer, or other steps. Additionally, steps may be performed in anysuitable order. As used in this document, “each” refers to each memberof a set or each member of a subset of a set. It is intended that theclaims and claim elements recited below do not invoke 35 U.S.C. 112(f)unless the words “means for” or “step for” are explicitly used in theparticular claim. The above described embodiments, while including thepreferred embodiment and the best mode of the invention known to theinventor at the time of filing, are given as illustrative examples only.It will be readily appreciated that many deviations may be made from thespecific embodiments disclosed in this specification without departingfrom the spirit and scope of the invention. Accordingly, the scope ofthe invention is to be determined by the claims below rather than beinglimited to the specifically described embodiments above.

What is claimed is:
 1. A two leg system, comprising: (a) a first legmechanism that includes a first upright bar that moves vertically inresponse to an amount of tension applied a first cable; (b) a second legmechanism, reflectively disposed oppositely from the first legmechanism, that includes a first upright bar that moves vertically inresponse to an amount of tension applied a first cable; and (c) anactuator that applies tension to both the first cable and the secondcable.
 2. The two leg system of claim 1, wherein the first cable iscontinuous with the second cable so as to form a continuous cable andwhere each of the first leg mechanism and the second leg mechanismcomprise: (a) a first platform coupling joint and a second platformcoupling joint spaced apart from and disposed below the first platformcoupling joint at a first distance; (b) a first lateral bar having aproximal end and an opposite distal end, the proximal end rotationallycoupled to the first platform coupling joint so that the first lateralbar is rotatable about the first platform coupling joint and isconstrained to movement along a predetermined plane; (c) a secondlateral bar, disposed below the first lateral bar, having a proximal endand an opposite distal end, the proximal end rotationally coupled to thesecond platform coupling joint so that the second lateral bar isrotatable about the second platform coupling joint and is constrained tomovement along the predetermined plane; (d) an upright bar including afirst bar coupling joint and a second bar coupling joint spaced apartfrom the first bar coupling joint at the first distance, the distal endof the first lateral bar hingedly coupled to the first bar couplingjoint and the distal end of the second lateral bar hingedly coupled tothe second bar coupling joint so that the first lateral bar, the secondlateral bar and the upright bar are constrained to movement along thepredetermined plane; (e) a passive device configured to apply force tothe upright bar; and (f) a cable affixed adjacent to a selected one ofthe first bar coupling joint and the second bar coupling joint andengaging the second platform coupling joint when affixed adjacent to thefirst bar coupling joint or engaging the first platform coupling jointwhen affixed adjacent to the second bar coupling joint wherein when thecable is drawn away from the upright bar, the cable applies inward forceto the upright bar and the upright bar moves in a first direction, andwherein when tension is released from the cable, the passive deviceexerts a force on the upright bar that causes the upright bar to move ina second direction that is opposite the first direction.
 3. The two legsystem of claim 2, wherein the actuator comprises: (a) a spool aroundwhich is wound a portion of the continuous cable; (b) a motor thatcontrols rotation of the spool; and (c) a controller that controls themotor so that when the spool rotates in a first rotational directionboth the upright bar of the first leg mechanism and the upright bar ofthe second leg mechanism move upwardly and when the spool rotates in asecond rotational direction opposite from the first rotational directionboth the upright bar of the first leg mechanism and the upright bar ofthe second leg mechanism move downwardly.
 4. The two leg system of claim3, further comprising a lateral track to which the spool is mounted andalong which the spool is configured to move, so that when the spoolmoves along a first direction along the lateral track the upright bar ofthe first leg mechanism moves upwardly and the upright bar of the secondleg mechanism moves downwardly, and so that when the spool moves along asecond direction along the lateral track opposite the first directionthe upright bar of the first leg mechanism moves downwardly and theupright bar of the second leg mechanism moves upwardly.
 5. The two legsystem of claim 4, further comprising: (a) a sensor for sensingelevation of a surface below each leg; and (b) an actuator for movingthe spool along the track, wherein the controller is responsive to thesensor and configured to determine a differential extension between theupright bar of first leg mechanism and the upright bar of the second legmechanism so that the first leg mechanism and the second leg mechanismeach conform to the surface, the controller also configured to adjustthe actuator to move the spool to a position that achieves thedifferential extension.
 6. The two leg system of claim 5, wherein thesensor comprises a selected one of a contact sensor or a roll indicator.7. The two leg system of claim 2, wherein the passive device comprises alinear spring coupled between the first platform coupling joint and thesecond bar coupling joint.
 8. The two leg system of claim 2, wherein thepassive device comprises a spring selected from a list of springsconsisting of: a coil spring, a gas spring and a torsion spring.
 9. Thetwo leg system of claim 2, wherein cable is selected from a list ofcable types consisting of: a steel cable, a rope, a wire, a cord, aline, and a strap.
 10. The two leg system of claim 2, wherein when thecable is affixed adjacent to the first bar coupling joint and engagesthe second platform coupling joint, the upright bar moves downwardlywhen tension is applied to the cable and moves upwardly when tension isreleased from the cable, and wherein when the cable is affixed adjacentto the second bar coupling joint and engages the first platform couplingjoint, the upright bar moves upwardly when tension is applied to thecable and moves downwardly when tension is released from the cable. 11.The two leg system of claim 2, wherein the first platform coupling jointand the second platform coupling joint are affixed to a frame.
 12. Thetwo leg system of claim 11, further comprising a shock absorber affixedto the platform and affixed to an end of the cable and configured toabsorb shock from the cable.